When I change the RB2 position settings to fullback in my formation settings menu, my fullback gets zero carries, even when I change the carry percentage to 50/50. The only way I can get my fullback any carries is to list him as RB2 on my depth chart and leave the formation settings alone.

I have not had this problem.. As long as he is listed as the Full Back on the depth chart and the Full Back is set on the formation and you make sure to specify that the fullback will take a certain percentage of the carries he should do it.